FIGS. 9 and 10 show a conventional metal core for a rubber crawler and a rubber crawler in which a plurality of the conventional metal cores are embedded. As shown in FIG. 9, a metal core 101 comprises an engaging part 102 provided at the center thereof for engaging a sprocket, roughly rectangular horn members 103, 104 provided laterally outside the engaging part 102, and right and left wing portions 105, 105 extending at the outsides of the horn members 103, 104. A plurality of the metal cores 101 are embedded at a fixed interval, with the horn members 103, 104 protruding out of rubber material R. An engaging hole 106 in which a sprocket tooth is inserted for transmitting driving force is provided between the adjacent metal cores 101, at the middle of the width direction.
When a rubber crawler travels on uneven ground, sand is taken in on the inner circumference of the rubber crawler. In the conventional rubber crawler, sand is hardly discharged to the outside, because an interval L between adjacent metal cores and an engaging hole 106 are both small. Especially, sand often stays at a space M between horn members 103, 104, because the space M engages with a sprocket s with a slight gap. When the sprocket s engages the engaging part 102 of the metal core, sand is stamped down therebetween, and stored up on the engaging part 102. In consequence, the circumference of the rubber crawler is elongated by the stored sand, thereby causing excess tension thereon. This breaks steel cords and disables the rubber crawler from traveling. Besides it has bad effects on the machine.